Non-Hodgkin's lymphoma (NHL) rates have been increasing since the 1940s. Incidence is lower among women than among men, yet few risk factors explain incidence patterns over time or by gender. One possible exposure that may explain differences in risk patterns of men and women is hormone therapy (HT). Our own prior research suggested HT and other exogenous estrogen exposures decrease women's risk of high and intermediate NHL, yet results of another study suggest HT increases risk of follicular NHL (a subtype we did not study). Both studies had limited information on potential confounders of an HT-NHL relationship; nevertheless these results are intriguing because the evolution of cell type may depend on B-cell maturation and differentiation which is influenced by levels of interleukin-6 (IL-6); these, in turn, are influenced by the individual's IL-6 genotype and may be impacted by estrogen and progesterone exposure. We propose to conduct a population-based case-control study of B-cell NHL among women 20- 79 years of age, living in Los Angeles County, who are English speaking. We will recruit 1173 cases and 1173 controls, who will provide information during an in-person interview and will provide a buccal cell sample. Cases will have a first primary NHL diagnosis that occurs between July 1, 2004 and December 31, 2007. Controls will be frequency matched to cases by age (5 year age groups) and race/ethnicity and will be identified by surveying the neighborhoods of cases. In this study we will address 1) whether HT use (including specific types, durations, ages and recency of use) affects NHL risk; 2) whether oral contraceptives (including types, durations, and ages of use), lactation suppressants or other exogenous hormones affect NHL risk; 3) whether NHL risk associated with use of exogenous hormones varies by histologic subtype; 4) whether IL-6 genotype (as defined by 4 polymorphisms) modifies any of these relationships; and 5) whether reproductive factors, medical exposures or lifestyle characteristics influence risk of NHL.